3,5,6-Trichloropicolinic acid is a known compound useful as a herbicide and as an agent for the control of pig ascarids. The compound is a white solid melting at 164.degree.-165.degree.C. and is of extremely low solubility in water and petroleum oils and of moderate to high solubility in common organic solvents.
Collins et al., J. Chem. Soc., (c); pages 167-174 (1971) teach that halogens ortho and para to the ring nitrogen in pentachloropyridine are reactive with hydrazine hydrate. This reference further teaches the formation of tetrahalo-4-hydroxy pyridine from the action of aqueous sodium hydroxide on tetrahalo-4-hydrazino pyridines. From this same starting material, 2,3,6-trichloropyridine is formed from the reaction with cuprous oxide in hot water.